Thermal equipment, particularly thermal equipment in use in the food industry, will ideally require as precise a thermal and humidity control as possible. One problem involves the control and duplication of several pieces of equipment which may work against each other. Where each piece of equipment is separately contained and operated, the potential problems multiply, including more replacement parts, more electrical connections, more control electronics and the like. The more unified a series of equipments become, the more efficient is the overall operation.
Balancing energy in terms of utilization should also be considered. For example where one piece of equipment has a required ease of transport of food, most such equipment must have high user access, typically a rack of trays for quick removal for use in loading, bringing to temperature and maintaining temperature. Tray loading and storage usually requires a wide opening such as a door which provides a continual stream of upset to the internal environment and to the overall energy environment. A unit of equipment needs to have the ability to adjust from a condition of intermittent and continual usage. The food items recently added should come to a good temperature and humidity condition quickly, and the overall burden on the energy system should be eased.
Complicating this goal is the physics associated with the inside of the unit of equipment. Where hot air sources and heating elements are present, there is a danger that the dry heat will harden the food, and that the moist heat will condense on the food to make the food soggy. These are the extreme limits of wrong operation. More common are the closer limits of wrong operation in that food on horizontal racks for example, in the upper reaches overheats and dries out, whereas food on the lower reaches experiences condensation and is too cool.
Another problem is the delay time in bringing the food to temperature and humidity. Where electric heating of a separate water tank is used to provide steam or vapor, the electric elements have to be turned on well in advance of the actual need for the vapor, so that the electric elements can heat, followed by heating of the surrounding water, followed by a rise in temperature as to permit vapor and steam to be used.
The ability to use a large mass of water held at the optimum temperature is limited for many reasons, not the least of which is equipment spacing requirements, equipment designs militating against the proper proximity and orientation, and fact that current designs provide for limits based upon the surface area of containers, and typically provide a volume, mass and control scheme to serve specialized containers.
Physical and scientific limitations on multiple pieces of equipment are not only difficult to maintain, but monitoring in order that control may be effected is also problematic. In terms of moisture and humidity, temperature probes without more don't indicate moisture. One hundred eighty degrees of moist heat can cause heat and moisture penetration into food to bring the food to its final heated and moist condition more quickly. The same temperature of dry heat could cause hardening and spoilage of the food in a fraction of the time.
Distribution of heat is another problem. Where a pan is heated, no benefit is had unless it is certain that water is present, and unless it is certain that the humidity reaches the other areas of the cabinet. Where a dry heating element is energized, the amount of heat leaving the element before shut off depends upon the moisture, and therefore total heat capacity of the volume of air in the unit of equipment. Thus, temperature alone will not give an indication of how much thermal energy has been introduced. Humidity alone will not give an indication of how much thermal energy has been introduced, and neither will it enable a projection based upon usage of the equipment for quick additional moisture and thermal input.
Another problem with conventional equipment configuration is the vented cabinet. Where a vent is provided, the cabinet continuously emits a mixture of moisture and air to the surrounding room representing losses in energy due to the raised temperature of the exiting components compared to ambient temperature, and the energy which must be added to vaporize water to replace the humidity lost from the vent. Vented systems also have a physical limitation as to where they can be placed to insure that the vented exit does not cause condensation on other equipment or walls, and that the condensation exit is not blocked as it would upset the steady state temperature and moisture movements within the unit, and likely cause the food to become water laden or soggy.